Technical Field
Aspects of the present disclosures relate to an image scanning apparatus.
Related Art
An image scanning apparatus configured to store, in a non-volatile memory, white reference data obtained by scanning a white reference plate and to perform shading correction using the stored white reference data is known. In the image scanning apparatus, a contact type image sensor including a light source, a rod lens array and photoelectric conversion elements is used. It is known that, in such a contact type image sensor, larger amount of light is collected in a central portion of each single lens of the rod lens array and smaller amount of light is collected in a peripheral portion of each single lens of the rod lens array. In addition, in the contact type image sensor the position of the rod lens array and the position of the photoelectric conversion elements may shift with respect to each other due to a difference in expansion coefficient or a difference in fixing manner between a board mounting the photoelectric conversion elements and a board mounting the rod lens array.
The above described conventional image scanning apparatus is further configured to calculate, in regard to a particular number of photoelectric conversion elements disposed within an interval between adjacent lenses of the rod lens array, the maximum value and the minimum value of image data obtained by performing shading correction using the stored white reference data so as to decrease a scanning error due to the above described position shift. The image scanning apparatus determines the scanning start position being a pixel position at which the scanning is started so that the difference between the calculated maximum value and the minimum value obtained while shifting the scanning start position pixel by pixel is minimized.